Your question is answered in the text of its asking.
According to the Catholic church everyone has a Guardian Angel.
That is correct. (CCC 334-336)
Two persons, one marriage
What happens when you get married?
Per the scripture you quoted "two become one flesh." That uniting during the sacrament of marriage is something that happens on earth, between two persons, unified beings that are both spiritual and corporeal.1 Angels are beings of spirit. There is no reason to presume that they are affected by that, nor that their guardian role does not remain to be fulfilled.
When the Bible says married couples “become one flesh,” that is a way of saying that (1) there is a level of carnal intimacy that is only possible in a marriage, and (2) therefore, the marriage union is indissoluble. (Catholic PoV)2. It does not mean that the man and woman cease to be two distinct persons. Each person has their guardian angel.
Angels as beings of spirit, per my reply to your recent question here
'Angel' is the name of their office, not of their nature. If you seek
the name of their nature, it is 'spirit'; if you seek the name of
their office, it is 'angel': from what they are, 'spirit', from what
they do, 'angel.'"
According to Catholic belief (and indeed, a lot of Christian belief) the flesh and the spirit are two domains that overlap (or are as above, unified) during a person's life here on earth. The flesh in time ends, at death, whereas the spirit is eternal.
1,2 Assistance in how to phrase this from @AthanasiusOfAlex