I annoy myself being so jealous, help!

Okay so, me and my boyfriend have been going out over a year now and we are really close, see each other everyday at college, go round to each others houses etc. We started back at college in September and I've been fine, no jealousy, understanding that he loves me so that's all that matters.

Then yesterday, I was walking to class and this girl (who I had this same problem with last year) ran in front of me, past me and jumped to grab my boyfriends bag and shoved his shoulder in a flirty way, it wasn't pleasant to watch. It made me really upset and vulnerable.

It wasn't his fault because he wasn't expecting it so I cant be annoyed at him, I'm more annoyed at myself for letting it get to me any suggestions on what I can do to get over this problem please?