There are a lot of things you should look at in a composite chart that can be good signs and the relationship has a chance, or bad signs and the relationship may struggle. One of the difficult signs is when you have many planets in one sign or one house in the composite chart. In a natal chart, this would be considered a stellium, which isn’t necessarily a bad person for an individual if they can learn to channel the energy in a positive way. But in a composite chart, it’s an entirely different matter.
A composite chart merges together your chart and the chart of another person to create a new chart for your relationship with one another. It shows areas of strength and weakness in your relationship, and how the two of you come together. When you have many planets in one sign or one house in the composite chart, what this can show is that there’s too much focus in one part of the relationship. This can create an unbalance in the relationship. Ideally, you want to see planets nicely spread out in a composite chart so there’s somewhat equal balance within the relationship. 2 or 3 planets together may not be too bad, but 4 or more in one sign or house can be problematic.
The sign or house that has this overabundance of energy can suck all of the energy out of the relationship, and very important aspects of the relationship can be ignored because of that. You may find that there’s an intense connection between the two of you (in what way can depend on the sign/house involved), and this may draw you together at first. It can be exciting and passionate, especially in fire or water signs or houses. But after a while, it can become draining, on each of you and on the relationship itself, and it can almost be like the relationship swallows itself whole as that one focus acts a little like a black hole, sucking everything into it.
How it impacts each of you can be seen through how that energy interacts with each of your individual natal charts. It can be most impactful if it’s conjunct your natal Sun, Moon, one of the angles, or falls in your natal 1st house, and the relationship can really have a hold over you. If it’s square or opposite a lot in your chart, you can struggle with the energy, but you may be more likely to walk away, whereas with a conjunction, you may be more likely to try and stick it out, no matter how bad it may be for you. If it’s sextile and trine a lot in your chart, you may have a chance to try and work with the energy. But that’s very difficult to do, and requires some serious, conscious effort on both of your parts. You need to give each other the ability to be individuals so you don’t get lost in the hyper energy of the relationship, you need to make sure you’re not ignoring anything important together, and you need to find some way to channel the energy positively.