Is the word 'douloo' (the word used in 1 Cor. 7:15 = 'under bondage') ever used in the literature of the day in reference to the marriage bond, or to indicate freedom from the marriage bond? I hold the same view that you do, namely that this verse does grant freedom to remarry. But one gentleman who is giving me feedback at present, who does not believe this, has said that he might be convinced this verse does give freedom to remarry if it could be shown that dedoulotai is used in reference to the marriage bond in other literature of the time.
Reply: Your friend is right - douloo seems very strange to us when it is used in this context, because it implies bondage to slavery. However it is no less strange to our minds that the use of eleutheros ('freedom') being used used in a marriage context in (in 1Cor.7.39; Rom.7.3), because this word means 'freedom from slavery'. The reason is, I think, that Paul is alluding to the context of Ex.21.10f, where the standard grounds for divorce are based on the rights of the least important married person in society - ie a wife who is a former slave. For details see the end of the article here.