The first sentence could be interpreted in two different ways depending on context:
- I love you more than I love Tom. (most likely the correct definition)
*Think about this example: "I like playing soccer more than basketball." This does not mean "I like playing soccer more than basketball likes playing soccer." The real meaning of this is, "I like playing soccer more than I like playing basketball." The second "I like" has been omitted from the first sentence, similar to how the second "I love" has been omitted from the original sentence.
- I love you more than Tom loves you.
*Using the original sentence to get this point across is not ideal, as the meaning may be ambiguous. If this were the meaning of the sentence, it would probably be stated as, "I love you more than Tom does," which is equivalent to, "I love you more than Tom loves you."
The second sentence is just how it is stated:
I love you more than Tom loves you.
So, in most (if not all) instances, the two original sentences have different meanings.