Astralplane,
I'd say be careful, because he has a girlfriend:
a) If he loves her ==> you lose.
b) If he is bored + a cheater ==> he will leave her for you, but then he will tend to feel bored ==> you lose. SEE BRANGELINA : Brad left Jennifer Aniston for Angelina, but then he cheated on Angelina for another (or many others???)
Now, here's your answers:
1. Your synastry is great = mutual appreciation. Sun, Moon, Venus, Saturn, mostly in positive aspects = you've got such a strong chemistry, and deeply identical emotions.
2. However, your sun is in pisces makes you a dreamer, and transiting Neptune will cloud both your judgement (dreamy state, not in touch with reality), but also his venus (super-idealized love). When the transit is over, you may not feel the same way.
3. your natal venus is in close conjunction with mars. this means that you are extremely passionate + go-getter in love. if you like someone, nothing can stop you. On the other hand, his Cancer moon makes him more shy, or reserved.