Paul Nassif -- I'm Cool with Adrienne Maloof Dating Sean Stewart

Paul Nassif is taking the high road -- rather than bashing his ex, Adrienne Maloof, for dating a much younger man ... he's just happy that she's happy.

Maloof has been seen all over town this past week with her new beau, Sean Stewart, who happens to be 20 years her junior.

But when we saw Nassif last night at RivaBella in West Hollywood, he acted like a perfect gentleman, saying, "As long as she's happy, that's all I care about."