There are no marriages performed in heaven, you are correct. Marriage is an ordinance that needs to be performed on earth. If it is performed by one who has the sealing power given him by God, then it is sealed for eternity. These are the words of Christ given by revelation and found in Doctrine and Covenants, Section 132 (the greatest kingdom of glory is the highest kingdom of the Celestial kingdom, mentioned by Paul, and is where God’s full presence is found):

Therefore, if a man marry him a wife in the world, and he marry her not by me nor by my word, and he covenant with her so long as he is in the world and she with him, their covenant and marriage are not of force when they are dead, and when they are out of the world; therefore, they are not bound by any law when they are out of the world.

Therefore, when they are out of the world they neither marry nor are given in marriage; but are appointed angels in heaven, which angels are ministering servants, to minister for those who are worthy of a far more, and an exceeding, and an eternal weight of glory.

And again, verily I say unto you, if a man marry a wife, and make a covenant with her for time and for all eternity, if that covenant is not by me or by my word, which is my law, and is not sealed by the Holy Spirit of promise, through him whom I have anointed and appointed unto this power, then it is not valid neither of force when they are out of the world, because they are not joined by me, saith the Lord, neither by my word; when they are out of the world it cannot be received there…they cannot therefore, inherit my glory; for my house is a house of order, saith the Lord God.

And again, verily I say unto you, if a man marry a wife by my word, which is my law, and by the new and everlasting covenant, and it is sealed unto them by the Holy Spirit of promise, by him who is anointed, unto whom I have appointed this power and the keys of this priesthood;…therefore shall they be from everlasting to everlasting.

For I have conferred upon you the keys and power of the priesthood, wherein I restore all things, and make known unto you all things in due time.
And verily, verily, I say unto you, that whatsoever you seal on earth shall be sealed in heaven; and whatsoever you bind on earth, in my name and by my word, saith the Lord, it shall be eternally bound in the heavens;

“If a husband to whom one is sealed dies, a wife can remarry civilly. Her sealing to her late husband is in tact forever, should they both desire it, and conditioned upon both of them having remained true to those covenants. They will unite eternally after death.”

unite in what?
our covenant in Marrage is only here on earth.
there will no marrying after we die, becuase in heaven
we will become brothers and sisters becuase we are all son’s and daughthers of God.
Jesus dn’t mention the word seald or eternal covenand in theire marrage life, the only way to be free in marrage law if the husbond or the wife die one of theme can marry again. (Rom.7:2)

34 Jesus replied, “The people of this age marry and are given in marriage. 35 But those who are considered worthy of taking part in the age to come and in the resurrection from the dead will neither marry nor be given in marriage, 36 and they can no longer die; for they are like the angels. They are God’s children,“ ( Luke 20:34-36)

If a husband to whom one is sealed dies, a wife can remarry civilly. Her sealing to her late husband is in tact forever, should they both desire it, and conditioned upon both of them having remained true to those covenants. They will unite eternally after death.

In the case of suicide, or in delicate situations that involve one party desiring the sealing and the other not, these are matters to be addressed with individual local leaders. Where those leaders deem it appropriate, they will ask questions of the First Presidency of the Church to resolve matters that are particular to an individual case, by revelation and on behalf of the Savior.

If you are a member of The Church of Jesus Christ asking these questions, we would refer you to your local leaders who can provide more official and detailed answers to your sincere questions. If you have other questions for us, or about our faith in general, and are a friend of another faith, we invite you to share those as well.

The Lord has only the perfectly best thing in mind for each of us, and apostles of the Lord in our day have reiterated that no one will be forced to be with a companion eternally that they don’t want to be with.

Wishing you the best in your spiritual journey,