This is a two-part thing, hence the title and I couldn't come up with a shorter topic name.
So I'm in a conundrum. Remember how I was talking about being honest with my guy friend who is the Sagittarius Sun that I found him attractive? We kind of got into a conversation yesterday after I sent him Guinness beer memes because he loves drinking the stuff and I started joking that I wouldn't know what Irish foreplay was and I'd have to find an Irishman to find out after joking that Guinness was considered Irish foreplay. I continued joking that it wouldn't take much to get an Irishman into my pants if they had the right personality and humor. This Sagittarius friend is Irish American. And I'm attracted to his personality and humor.
I think I might have given him the wrong idea or made an assumption after I said he was safe from being in that category.
And that's mainly because I don't want to ruin a good friendship.
I clarified that while I found him very attractive, it didn't mean it was mutual on his part because I'm being respectful regarding that. And I'm okay with there not being a mutual attraction. If he's not attracted to me, my feelings won't get hurt because I understand that I'm not everyone's cup of tea. What threw me off a bit is that he never responded to what I said. He saw it but didn't say anything.
I think I might have put him in the friendzone, if that's a real thing, but I'm honestly just being respectful of him not being attracted to me. Like I stated before, my feelings won't be hurt if he's not and I do enjoy being friends with him otherwise.
I'm just confused on the no response because I've heard that him not saying anything is a response itself.
That brings me to the second part because I am curious about it. What would indicate mutual attraction in astrology/synastry? Is it Venus, Mars, Moon, and Pluto connections?
One cliche is that a man's Moon sign is compatible with a woman's Sun sign, and vice versa. I'll let other people go deeper into this!
I read that was a marriage indicator. And I'm sure that's a cliche. But then again, I've never had a man's Moon conjunct my Sun or aspecting my Sun in anyway. Just Venus and I actually love that aspect, especially the conjunction. Lol.
Update: Was joking around again with him today regarding a hot dog/sausage image I sent for fun where the hot dog was happy with a grin on its face and standing up mostly straight and giving a thumbs up. Some of my messages made me sound pervier than I intended and it was not intentional and somehow his mind ended up taking it that way too and a couple of his responses were kind of pervy as well. It was just banter between friends, really.
I had to warn him that our joking around was getting close to flirting territory.
His response? "Blah. Apparently everytime I speak I'm doing that so er yeah lol".
And apparently he's very aware of things he says or types can be perceived. I learned that after I mentioned to him that it seemed like he made it sound like he was aware that it was going in the flirting territory direction.
I think I need to learn to tap into my Mars in Sagittarius energy because it seems like he was trying to flirt. I feel mortified that I didn't realize until after the fact, mostly I'm not good at picking up on people flirting with me.
I'll vouch for a man's Moon with the gal's sun - that's me & my guy 
This will be generic but it's also what I've actually experienced
1) Sun & Moon aspects, conjunction most powerful
2) Mars/Venus aspects - every which way - ie not just Mars to Venus, but Mars/Mars & Venus/Venus. To be honest I also look at elements - even if not exact aspect, two air signs, for instance Venus in Libra, & the other has Mars in Gemini - that's sympathetic energy there, I wouldn't discount it
3) The angles - such as your ascendant being his IC etc, also planets in the angular houses - your planets (especially Sun/Moon/Venus/Mars/Moon) in his first or 7th for example
4) Sign & ruler on descendant - are there harmonics, sympathies, aspects between them - ?
5) The sign/ruler of Mars/Sun if a female, Venus/Moon if male - again, doesn't have to be a straight out correlation - for instance, if you've got Mars in Gemini you may find yourself attracted to someone with a packed third house
As far as longevity - I'd look to a mix of hard/soft aspects, strong Saturn aspects, and/or nodal connections
To use my relationship as example:
Virgo Sun with his Virgo Moon
My descendant is his IC
My descendant conjuncts his mars & Venus
Rulers of descendant in aspect, also a 'harmony' in that Uranus is in my 7th, his descendant is Aquarius (Uranus ruled) - a side note, our Uranus's are conjunct, which are conjunct his Venus (which is on my descendant angle) & sextile my Venus(rules my descendant) - we met when I was just beginning my Uranus opposition! & believe me right when I finished mine his was officially starting - it's been a crazy ride. & you can see that our relationship was 'destined' to be Uranian, & we are 'built' for it: ie, our 7th house/descendant signatures
His ascendant is my Moon & Venus sign & both are in his first house
His Saturn conjunct my moon
My Saturn squares his Venus
Mars trine Mars
Venus sextile Venus
Mars & Venus in same element ( a bit wide for an official trine)
He has a stellium in Libra, I have descendant libra & Venus is my final depositor & very strong in my chart, I'd say I have a 'venusian' character
I have Mars in Gemini - he has a packed third house, his Mars is in Libra (also just within 3rd house)- again an air sign harmony
My two cents, hope helps
Now, now, Scorpio rising! You naughty one! 