husband thinks 3ways are normal

hi I've been with my husband 16 years married almost 11. during dating every six months he'd break up with me go be a stupid guy sleep with someone else then want me back. I know I'm dumb. we got married at 21 I wanted to start a family a year later he breaks up with me telling me he doesn't want children and if he had them they'd be an accident. so imagine my surprise that a week later he's moved in with an ex who's 8 months pregnant ( no the baby was not his, this girl was a huge whore and had a new guy living with her every month) as soon as that girl got close to her due date guess who wants to come home. yep and I let him. we move away to be closer to my family things are going great so at 24 we welcome our first daughter, and she is perfect. we're fine we buy our first home he's working 2nd shift to move up in the company. it takes a bit of a toll and we're only having sex sometimes once a week. on our daughters 4th birthday he comes back from a business trip and he cheated. I was devastated. cause to me he didn't just betray me he betrayed our daughter. we start therapy, he's also diagnosed with depression. the next year I find out he went on POF and thought he saw a woman from my mommy group looking to cheat so he finds her on FB and texts her. needless to say it's not her and she texted me everything. back to therapy we go! then it takes 2 years for me to feel comfortable enough to have our 2nd daughter. well she's here now and 7 months old. we just went on a family vacation and the whole trip I was like a single mom. he was always missing he's the same way at home and he says he wants more kids. but when we get back from our trip I ask what is up with him and he says I need you to spice up our sex life. he wants me to put my kids to bed and sneak another girls in to have a 3way or he wants to watch some guy have sex with me. this isn't the first time he's brought this up, every 6 months he pulls this shit and I tell him to get out then he mopes around for a day or two then says I didn't mean it I was in a bad place we should just try different positions and changes things for us. he has to go out of town twice next year. the way he talks about this stuff disgusts me. I don't know what to do anymore. therapy doesn't seem to help, medicine. I don't think he really loves me or the girls cause he does nothing a husband should do other then going to work and paying bills. if he's not at work he's sleeping. I need advice