I believe that there are two forms of relationship (not mutually exclusive) that can each be vehicles for the holy, and worthy of being blessed by the church.
The first is a Covenant, entered into for the mutual affection, aid and support of the parties concerned. This can be male and female, gay and straight, short and tall, of all different sorts. The important point is the nature of the relationship to be affirmed, which is for the relevant parties to decide, and that they wish the relationship to be affirmed and given support and substance by God.
The second is a Parenting Bond – that is, when two people come together and wish to form a family. This is (in origin) something which is only available to a male/female couple even where, for all sorts of other reasons, there are now other forms of parenting. I believe that the wider society has a strong and legitimate claim to be involved in this form of relationship, given the consequences of poor parenting upon that wider society, and that this form of relationship is therefore distinctly different to the first.
I believe that the wider conversations on this topic are bedevilled by a failure to distinguish between these two forms of relationship. It doesn’t matter to me which one gets called by the ‘m’ word, although I suspect a lot of hassle could be saved by keeping it for the second. That’s not a theological point though.