Ok, after reading the above responses this could easily get sidetracked talking about which old laws to follow and which not to. We can hopefully avoid this if we can all agree that there are plenty of good christian people who do not follow every one of the laws in the OT.
Regarding the claim the NT is clear on homosexuality - prove it! Here Mii's argument is compelling, no need to reiterate because "it is written" - yes I'll pay that, but read my paragraph above...
Regarding the claim that marriage is clearly established as being between a man and a woman, I have no idea what bible you've been reading. It is clearly established between a man and a whole lot of women. Since Abraham was mentioned, he had at least two wives and a few concubines.
What is also clear from the responses is that this particular law is singled out because homosexuality is "icky". Fine, but is that reason to shun a family wedding? I like durian and brussels sprouts (not together
), my kids think that's icky, who cares? When talking about driving a wedge between family it's not about you and your judgements it's about god.
@RickyZ If you miss the wedding you can never go back and fix it. You will regret that for your entire life. After reading the comments so far I am convinced the arguments are weak and you should
DEFINITELY GO TO THE WEDDING!