What state are you in? How many years is considered a "long-term marriage" in your state? (In Florida, it is generally 15). If it's 10 in your state, you may have some leverage there.
If your husband is intentionally (or even un-intentionally) "under-employed," a good attorney can hire an occupational evaluator who can IMPUTE INCOME to your husband, based on what he SHOULD be earning, based on his experience, qualifications and the availability of those types of jobs in your area. You would probably have to pay the up-front cost of the OE, but it might be well-worth the investment.
As for your "how," don't overthink it, JSTV. He's a guy, in lust with a younger girl. Do I need to spell it out for you? He's running on LUST right now, and it's highly addictive. I'm not EXCUSING it, mind you, as i have ZERO RESPECT for a man that would run out on his family, but I'm just trying to EXPLAIN it to you.
