OP, you have not responded whether you have been to survivinginfidelity.com yet.
Go now. Register. Post. It is not a 'family board,' so you can speak your mind (they are not anti-family, of course, it is just not their focus as it is here). You will get advice from people who have ALL been there, done that. Please do this now.
What will that get you? Affairs tend to follow a script. The lies, the excuses, the patterns, the behaviors, the things that are said...are shockingly similar from case to case. You need to be prepared. Seriously, it is like adulterers get a How-To Manual.
'I love you but I'm not in love with you'--this is CLASSIC, textbook cheat-speak. I read one psychologist who said that hearing this is second only to catching your spouse in bed with someone else as an indicator of an affair.
Tomorrow, go and buy the book Love Must be Tough by James Dobson.
You may or may not want to save your marriage but it is my opinion, and the opinion of Dobson and most on SI that the only way to have that option is to respect yourself, take care of yourself first, decide on your boundaries and communicate those to him, and then back that up with action.
If he is in an affair, he is NOT rational right now. You cannot reason with him. You cannot control his actions but you can control your own.
Right now you are the only one on your team. I'm sorry, but his actions are showing you that as well as his words.
Sorry this is so long. I don't mean it to be harsh but a helping hand from someone who never wanted to know this stuff.