Saw one of the teachers I used to really like?

It happened like 10 minutes ago, where we left the drive thru of macdonalds, I saw one of my chemistry teachers I really liked, he really liked me too, after school we went cinema, used to have a right laugh together, went to restaurants with me and my mum (when she wasn't drunk) and we'd just have a happy time together, until he said those words "I think we should be together..." He's 36 but my boyfriends 28, a little bit of age difference there, he's sitting with us right now munching on macdonalds, talking about life and watching eastenders, he messaged me on BBM with is number just 2 minutes ago, I kept it but I'm really confused, I'm not gonna cheat on my boyfriend but the teacher is trying his best to make our old bond stronger again...how can I cope with this??