Am right to feel this way?

Hi, I know this has been a week ago, but I'm sorry this happened to you. It is right for you to feel this way. However, feelings of resentment and anger is only temporary. Instead of wasting your time on him, find someone else. Your emotions will only get the best of you, so write, draw, listen to a song, and gather your thoughts together before exploding on him because there are better alternatives to this situation.

You should talk to him about this situation and express your feelings such as guilt and betrayal. If you want to continue seeing or even associating with him, it is your choice. I understand the latter, if you don't. He literally never spoke up about his affairs or that kind of stuff, but did he ever mention his motives on dating? Did he explain to you what kind of relationship he wants like a fling or one-night-stand? If so, you could've saw the red flags already there, but if his personality and looks attract you, you also need to look out for other details, further, into the conversations. I'm not saying you didn't, but next time ask more questions like "how do you feel about dating?" or "what are your thoughts on serious relationships?" However, it'd be more rude and intrusive if you blatantly asked them personal questions like "How many people did you sleep so far? Have you been with other women or are seeing someone else right now? How many exes do you have?" Honestly, this man didn't say anything else nor his motives maybe because you didn't ask him. On the other hand, he probably is hiding other secrets your close friend, your close friend's bf, nor you don't know about. Be aware and have a safe relationship.

P.S. I'm new to this relationship thing, but I've read some articles, read books, and observed other people. I understand this is more of an experience type of deal here, but these are a few basic understandings I've learned.
Hopefully you find someone best suitable for you and that you two live a long and happy life/serious relationship!

Send him a text saying that you have found out what happened and that it has smashed the trust you had in him and that he should have been honest to you about his past.. The tell him the relationship is over..

Then do what you have to do to avoid him and get over the disappointment..

yeah, your feelings are valid. people can't tell you not to feel this or that.