Did Porthos really love his mistress?

This is something that has bothered me throughout the book as the book does not really make it clear, and I kept going back and forth in my head about it but could not finally decide what I thought on the matter.

Porthos is portrayed as being very vain and prideful, rather concerned about his looks and image, and he has a mistress who is described as being quite unattractive, and who is really very poor, though Porthos has the impression that her husband has this secret wealth.

So I could never make up my mind, did Porthos ever truly love the lawyers wife? Or was it always just about the money, or at least his illusion to the money he thought was there. It seems to me if he only cared about the money he could have found a richer mistress. How did a person such as he even end up with such a woman? They seemed quite mismatched, and at first it seemed as if he was only using her for her money, and yet since he kept going back to her, and when he first went to their house he could see how desolate they were, so I wondered if there was some part of him that truly did love her.

Then at the end after her husband died he is getting ready to be married to her, was it just so he could get inside the husbands chest? Which proved not to have very much money in it after all. Or was there more to it then just that?

I am convinced he did. Not because it is in The Three Musketeers, because you're right, Dumas did not mention it. And readers can swing both ways (maybe he intended it that way so he could make a sequel), but if you read Twenty Years After it'll become clear.

Porthos might be vain, but he has a great heart and would never marry only for money. I think he best compares to a great big man with a child's heart: his heart is simple and is easily pleased so he never designs...

In The Three Musketeers all the seeds of the characters are there but they are not terribly much shown off in depth. To get a better view, read the two sequels, or 5 in some cases: Twenty Years After, The Vicomte de Bragelonne, (Louise de la Vallière and The Man in the Iron Mask). Particularly the last one is very very enlightening.