Your feelings are valid, and you should not only allow yourself to feel them but also be kind to yourself about this situation, which it does already sound like you have been. But there are certainly things you can take from this. The main is that if you're not in a relationship then everything you do together and say to each other should be seen in that context. I cannot speak for his motivations and whether he was stringing you along to get a boost to his own self esteem, but him saying I love you in the context of a friendship cannot mean what you want it to mean. Ditto the making future plans. When this situation comes back around either with this person or someone else, you have to understand that you are either in a relationship or you are not. If you are not, you are friends, and none of this stuff can be romantic in the way that you want it to be. For now, I think you need to make a decision about this guy. Things cannot stay the same. He has a girlfriend, so being with him doesn't look like an option. Which means you either need to continue the friendship and heavily moderate the flirting and the comments (and probably your contact with him), or you just distance yourself from him until you've had some time to adjust to this. Maybe even have no contact at all for a bit. It's your choice, but it genuinely looks like to me like the latter option is the better one here, because at the moment all this friendship is doing is hurting you. I think you need some distance from it to heal, recalibrate and figure out what you need it from it and him.