There is a website dedicated to astro matchmaking, see
http://www.starmatch.com/ I am not sure of the accuracy of their synastry, but you can join for free and I find it useful because you can also enter other's data for free and receive the site's assessment of synastry for friendship, love etc. However, take note, it sure lists a lot of synastry aspects that I
can't identify, even with liberal orbs, between charts. So, receiving a high number for someone you're attracted to is gratifying, but I wouldn't advise using this as a tool to make up your mind
You know what? I have my own theory that: of COURSE people that we attract have squares and oppositions to our planets in synastry! Attraction is a powerful thing, relationships bring out challenging aspects of ourselves and those we relate to, and we learn from relating, we don't generally just tend to sit there admiring how easy it is. It's often intense, confusing, exciting, frightening, risky, and a steep learning curve. To me, this experience sounds a lot more like a square, or an opposition, than a whole bunch of fat lazy trines. Sure, you need some mutual ground to hold things together, some commonality to refer to, some soft synastry for mutual empathy and understanding, but quite frankly, my lovers can square me any day (preferably with some softer planets, like a Jupiter maybe?)
Remember the fact that we tend to attract people whose elemental balance "balances" our own? Well, you can't generally have that without some hard aspects. As a Fire/Air type, I seriously lack Earth and find balance in an intimate partner far more Earthy than I. To my knowledge, I have never even been attracted to a guy who was not, on balance, a "yin" (feminine) astrological character.
Perhaps without some of those lovely soft synastry aspects I wouldn't find the basis of mutual understanding, but I wouldn't shy away from a just a few squares or oppositions
. Those people in my life with wonderful soft synastry and an elemental balance more like mine are very good friends, but not intimate parters. Perhaps that's just me!