I'm wondering about this, because I am not sure how radical and liberal and left are being conceptualised in this discussion.
Liberal feminists, if we take first wave feminism and subsequent liberal action in the 1970s, was about using the legal framework to create conditions of equality. Thus, in your situation, PD, this means that the legal framework exists so that you could, if you so wished, leave your marriage, access divorce, and expect an equal split of assets and an equal consideration of your case in family law (in practice this doesn't work, given the cuts in legal aid and the income disparity between men and women which still exists - but the liberal response here is surely to fight those cuts and income inequality, i.e. in legal term and political terms).
Radical feminism is about challenging the inherently gendered social norms within which we operate (in a more practical, on the ground manner), so in terms of marriage, it was about addressing issues of domestic violence, rape (within and outwith marriage), sexual discrimination and the gendered expectation that women were the mothers and homemakers etc. I am not sure which radical feminist publication (and I am taking second wave here, if you want to go back to the roots) ever said the only feminist response to adultery is to leave the marriage. The feminist response would be not to accept/ignore/condone - which to take the OP, PD, you have actually taken a very active position in responding in light of your own circumstances; and you are challenging accepted gender/social roles (by being financially independent, by holding the behaviour to account, by standing true to your own values (I need to come back to this, because it doesn't necessarily involve your DH having to agree with you).
The whole 'choice' view of liberal feminism is third wave neo-liberal feminism. To quote Nancy Fraser, neoliberal feminism is 'divorced' from social solidarity - thus, the whole 'choice' neoliberal conceptualisation of feminism is about women having access to the same goods, behaviours, choices as men (in a free market, capitalist economy). It it is a very recent capitalist view of feminism - the whole 'choice' agenda is neoliberal, it is not liberal. There is nothing you are doing, if one views it like that, PD which inhibits women from making a different choice.
If you want to think about the left as social solidarity, then you could argue that by challenging social norms within your marriage, you are challenging the position of women. It depends what you do when you stay in a marraige (or in Nooka and my experience, what you do when you start to reconcile). DS is climbing over me, so I hope that makes sense...