Bf legally married

My new BF is legally married(11 years). I'm 24 and he is 30.

He had his ex have been apart for over 2 years, she lives 3 hours away with their 2 kids and is in a committed and serious relationship for the last 2 years herself.

They don't divorce because she is on his insurance (military) and can't afford it in her own. It currently is paying for her infertility treatments. He also pays her car and anything else she needs. But, they use that in place of "child support" and he receives housing allowance to continue to love off post for a home for when the kids come. So he just pays it out of that.

They get along very well and I have met her, she is nice. It is just an odd situation. How would feel if you were in this position?

(They both agreed to file for divorce when the other half is ready to move forward with someone else in form of marriage.)