I don't know about how it works for Roly, but for me, too much need does start caging the love I feel. It constricts it because when I need a person like that, it suddenly becomes detrimental to not have that person, which creates a huge perception of risk and fear. If the love I feel starts moving too far into need, then it just becomes about me and my preservation and not about my partner. I then need my partner to be all these things or do all these things in order for me to be happy. And if my partner isn't those things to me or doesn't do things, it creates unhappiness. That never feels healthy to me because it means that I'm holding someone else responsible for my emotions and not taking responsibility for them myself.
Feelings are funny things. They change more from internal shifts than from external shifts. A person can feel compersion and love for their partner one day and jealousy and anger another with no change in how their partner is being towards them. So for me, unhealthy need starts to happen when we let go of our own responsibility for our emotions and put them in the hands of our partner. That's not the same thing as having deep love for a partner. That's also not to say that a partner can't hurt me deeply by what they do, but I will always own those feelings.
And also, I don't consider that kind of toxic need the same as understanding what needs we have ourselves as individuals and seeking out partners who meet those needs. When we seek such partners, we're still holding that responsibility ourselves. But if i said "This is the only person who can make me happy", well...that's just scary. For me, and for the other person, since nobody can really be entirely responsible for the happiness of another person outside of parenthood.