You can't really FORCE someone to do individual counseling, but considering his serial infidelity in your marriage, I think it would be perfectly fair for you to say:
"Unless you get some help for your issues, I can't feel safe in this marriage. When you don't take my needs seriously, I feel like the other shoe is always going to drop. If you don't get some help, I'm going to need to do what I have to do in order to protect myself."
You might also consider prefacing a talk with him with something like:
"(Husband), this isn't going to be yet another in a series of talks about your need to get some help for your issues. Consider this the first in a series of ONE. Look, you're an adult, and I can't control you, but I need to be clear with you. The man that I choose to be married to WILL be faithful and monogamous with me. The man I choose to remain with WILL do what he reasonably can to seek help for anything that's causing him to not be emotionally healthy, especially where it affects his faithfulness and monogamy to ME. The man that I choose to remain married with WILL respect me, and treat me the way that I deserve to be treated, not just as his wife but as a fellow human being.
Whether or not that man is YOU, why that's completely up to you. Please take the weekend to think about this, and let me know by Monday whether or not you feel this man can be you."
You may want to check out Pearlharbor's thread (she's in Piecing now) for specific advice on how she did this. Hers is a perfect example of distinguishing between ULTIMATUMS (which don't work), and BOUNDARIES (which CAN).
